1. Field of the Invention
Dietary fiber can be defined as including all the insoluble and soluble components of food that are not broken down by digestive tract enzymes to produce low molecular weight compounds that can be readily absorbed into the blood stream. Plant cell wall materials such as cellulose, hemicellulose, lignin, and pectins are the primary source of dietary fiber in human and many animal diets, along with gums, mucilages, and other carbohydrates. The maintenance of adequate levels of fiber is important for the proper health and function of the body. Low levels of dietary fiber are associated with increased risk of colo-rectal cancers, inefficient and irregular bowel function, and other digestive disorders. Diets high in fiber have been found to be useful in obesity control and weight reduction programs because of their high ratio of bulk to calories. For these reasons, the food and feed industries have turned to dietary fillers and bulking agents for supplying the fiber requirements demanded by the market.
2. Description of the Prior Art
Dietary fillers and bulking agents can be categorized by solubility. The soluble group includes primarily the gums, pectins, and mucilages. These materials can have a substantial effect on the functional properties of other food components, and therefore have limited application in many food formulations. The insoluble fillers which have played a major role in this field include alphacellulose and microcrystalline cellulose. Alphacellulose is produced by grinding ordinary, kraft paper pulp obtained by the sulfiting of hardwood. Consumer acceptability of this product has been limited to some extent by its objectionable texture and mouth feel. The cellulose chains of kraft pulp comprise both crystalline and amorphous regions. When treated with hydrochloric acid as described by Battista et al. in U.S. Pat. No. 3,023,104, the amorphous regions are hydrolyzed leaving particles of crystallite aggregates, otherwise known as microcrystalline cellulose. Thompson et al. (U.S. Pat. No. 4,307,121) discloses a method for converting relatively nonligneous cellulose material such as soybean hulls to a short fiber cellulose suitable for human consumption. The process involves heating these materials in a slurry with a strong oxidizing reagent such as chlorine gas, followed by an alkaline cook, to yield a purified cellulose product.
The desirability of reducing the caloric content of certain foods while simultaneously increasing their content of dietary fiber has led to the development of food formulations where calorie-dense components such as flour are replaced partially by low-calorie fillers or bulking agents, either alone or in combination with various gums. These formulations have for the most part been utilized in baked goods such as breads and cakes. For example, in U.S. Pat. No. 3,676,150, Glicksman et al. teaches the production of a yeast-leavened bread from a wheat flour substitute comprising by weight 1-10% of a cellulose gum, 30-70% starch, and 30-70% alphacellulose.
In U.S. Pat. No. 4,237,170, Satin shows the preparation of a high-fiber content white bread wherein pea hulls ground to a small particle size are substituted for 5 to 20 parts by weight of the wheat flour.
Glicksman, U.S. Pat. No. 4,503,083, teaches the preparation of a reduced-calorie cake from a composition containing up to 10% of a bulking agent consisting of citrus albedo, sugarbeet pulp, and/or pineapple core, alone or in combination with a variety of gums such as carrageenan, guar, gum arabic, locust bean gum, tragacanth, karaya, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, xanthan, pectin, alginate, and agar.
Breads are made from a yeast-leavened, wheat flour dough which relies heavily upon the continuity of a gluten network for its elastic properties. In the making of a low-calorie bread, fillers added to the dough must not interfere with either the gluten network or the activity of the yeast.
Cakes differ from breads in that they are formed from batters which are foamed by mechanical agitation (mixing) or chemical leavening systems. In adding a fibrous filler to the batter, the rheological properties must be maintained in order to preserve the foam structure responsible for the texture of the baked product.
Fillers have also been incorporated as the principal ingredient in liquid and solid formulations designed as low-calorie meals. These preparations typically contain caloric constituents only as required to augment the flavor and overall consumer acceptability.